Window-type semiconductor packages are advanced packaging technology, characterized by forming at least an opening penetrating through a substrate, allowing a chip to be mounted over the opening, and electrically connected to the substrate by bonding wires through the opening. Such a structure is beneficial for shortening length of the bonding wires, thereby making electrical transmission or performances between the chip and the substrate more efficiently implemented.
As shown in FIG. 4A, for fabricating window-type packages in a batch manner, it is usually first to form a plurality of lower encapsulants 10 on a lower surface 110 of a substrate 11. The lower encapsulants 10 respectively encapsulate bonding wires 12 formed through openings 111 of the substrate 11, so as to protect the bonding wires 12 against external impact or contaminant, and to allow chips 13 mounted on an upper surface 112 of the substrate 11 to be well electrically connected to the substrate 11 by the bonding wires 12.
In order to encapsulate the chips 13 mounted on the substrate 11 for protection purpose, as shown in FIG. 4B, during a molding process, the semi-fabricated package structure is placed in a mold structure composed of a top mold 14 and a bottom mold 15. The top mold 14 is formed with a plurality of upwardly recessed portions 140 for respectively receiving the chips 13. The bottom mold 15 is formed with a plurality of downwardly recessed portions 150 for being engaged with the lower encapsulants 10 respectively, with dimensional tolerance being around 1 mm spacing or clearance 16 between a pair of corresponding downwardly recessed portion 150 and lower encapsulant 10. When a resin compound e.g. epoxy resin (as indicated by arrows in the drawing) is injected into the upwardly recessed portions 140 during molding, mold flow impact of the resin compound would possibly cause cracks (indicated by corrugated lines in the drawing) of the chips 13 at positions corresponding to the spacing or clearance 16 between downwardly recessed portions 150 and lower encapsulants 10, due to lack of support from the bottom mold 15 to cracking positions of the chips 13, thereby making quality and yield of fabricated package products undesirably deteriorated.
Therefore, how to develop a mold structure for assuring structural intactness of chips during a molding process for encapsulating the chips, is a critical problem to solve.